Reliability and Validity of Quadriceps Muscle Thickness Measurements in Ultrasonography: A Comparison with Muscle Mass and Strength

Objectives: Measurement of skeletal muscle using ultrasonography (US) has received considerable attention as an alternative method of muscle assessment. However, intra- and inter-rater reliability remains controversial. Furthermore, there is no consensus regarding the relationship between muscle assessment using US and muscle mass or physical assessment. We aimed to verify the validity and reliability of muscle measurements using US and its relationships with muscle strength and physical assessment. Methods: The 22 participants were all healthy men. Quadriceps muscle thickness was measured by US by three different raters. Intraclass correlation coefficient (ICC) was used to assess inter- and intra-rater reliability. The maximum isokinetic strength of the quadriceps and handgrip strength were used as measures of lower and upper muscle strength, respectively. Leg muscle mass was assessed using the leg skeletal muscle index (SMI), measured by body impedance analysis, and calf circumference. Results: The intra-rater reliability was excellent which the ICC(1,1) ranges 0.957-0.993, and ICC(1,3) ranges 0.985-0.998. For inter-rater reliability, the values of 0.904 for ICC(2,1) and 0.966 for ICC(2,3) indicated excellent reliability. Leg SMI was significantly correlated with quadriceps thickness (r=0.36). Maximum isokinetic strength and handgrip strength showed weak but statistically significant correlations with quadriceps thickness (r=0.20, r=0.30, respectively). The correlation between quadriceps thickness and calf circumference was not statistically significant. Conclusions: Quadriceps muscle assessment using US is a valid and reliable technique for healthy individuals. Quadriceps muscle thickness was significantly positively correlated with upper and lower muscle strength and leg SMI. Muscle thickness assessment could replace full body muscle assessment in clinical settings.